Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!dali.cs.montana.edu!uakari.primate.wisc.edu!caen!hellgate.utah.edu!csn!kessner!david From: david@kessner.denver.co.us (David Kessner) Newsgroups: comp.sys.ibm.pc.hardware Subject: Re: Why buy a DX over an SX? Message-ID: <1991Apr23.000348.6644@kessner.denver.co.us> Date: 23 Apr 91 00:03:48 GMT References: <14534@encore.Encore.COM> <1991Apr12.162615.13529@holos0.uucp> <1991Apr21.203004.9909@unlv.edu> Organization: Kessner, Inc. Lines: 43 In article <1991Apr21.203004.9909@unlv.edu> whitney@reed.cs.unlv.edu (Lee Whitney) writes: >In article <1991Apr12.162615.13529@holos0.uucp>, lbr@holos0.uucp (Len Reed) writes: >) >) So what? You're running *all* 16-bit software and you want to know >) why having a a 32-bit data path doesn't buy you much? Windows puts >) the machine into proctected mode, but it doesn't use 32 bit mode. >) >Your statement is impratical and misleading. First, the 386SX DOES have a 32 bit data path or else it would not be a 386! It's bandwidth is only limited across the bus, and since 90% of 386 buses are 16 bit (ISA), most DX systems would not realize a tremendous advantage over SX's when using 32-bit protected mode software. > >A $200 cache may be worth a 25-30% performance increase, but the 5-10% increase of a DX over an SX with a 16 bit bus is probably not. Ahhh... No. The 386SX has an INTERNAL 32-bit data path, but a 16 bit external path. It also has 32-bit INTERNAL Address paths, but 24 bit EXTERNAL-- meaning that it cannot address more than 16 meg of RAM... The ISA bus has no baring on the performance of the CPU. On ALL 386 (DX or SX) systems the memory is not accessed over the ISA bus, but rather has it's own 'memory bus'. The 16-bit nature of the ISA bus is just one reason-- the 8mhz standard bus speed is the other. So, since we are talking CPU speed rather than I/O speed, we'll move on... There are two very important issues here: A) The difference between 'MS-DOS Programs' and Protected mode programs, and B) The 16/32 bit EXTERNAL buss's. If all you are doing is running 'normal MS-DOS' Programs then you are correct in saying that a DX is about 10% faster than an SX... But if you were running more 32-bit software, I'd expect closer to 70-90% improvement since the majority of your 'fetches' are 32 bits. So... If you are performance minded-- use a DX and run 32-bit, protected mode software. If you are budget minded, get an SX and run blah 'normal' software. Also, if you notice... Most of the 20mhz DX's are or have been discontinued, so the choice is clearer. 16 or 20mhz machines are SX's, and 25-40mhz are DX's. If all you are running is 'normal' programs, the biggest speed boost will be from clock speed... -- David Kessner - david@kessner.denver.co.us | do { 1135 Fairfax, Denver CO 80220 (303) 377-1801 (p.m.) | . . . If you cant flame MS-DOS, who can you flame? | } while( jones);